Plasma Ball

Edited by David Kang

Plasma Balls are novelty items that can be use to demonstrate scientific concepts.

Those Plasma Balls are really fascinating. There is a high voltage source
attached to the inner ball that causes a current to flow to the nearest point
with a lower voltage. The ball is filled with a gas that glows when it has
electricity flowing through it. When nothing is touching the ball, the current
just flows anywhere onto the ball. When you touch the ball, some of the current
can flow through the glass and into you. Because your body is providing a place
for the current to flow, the electricity keeps flowing and the lines of current
can stay connected to the point on the ball that you are touching.

Needed: Plasma Ball
Fluorescent light bulb
Warnings: The plasma ball is usually harmless, but I would still recommend
warning those with any type of heart condition.
What to do: Place your hand on different spots of the sphere. It will collect
more "sparks" than the rest of the sphere. Also, place the fluorescent bulb next
to the sphere. It should light up. By holding the bulb in different places, you
can show that the electricity is actually moving from the sphere to you. If you
hold the bulb in the middle, only half of it will light. On the other hand, if
you hold the bulb at one end, the entire bulb should light up.
What to say: The plasma ball is the same concept as the Van de Graaff generator.
Instead of discharging from a large sphere to a smaller one, the plasma ball
discharges electricity from a small center ball to a larger surrounding sphere.
The sphere is filled with a gas that emits light of different colors as
electricity is passed through it.
The Physics: The plasma ball uses fluorescence to produce the different colors
of light. Fluorescence occurs as electrons pass through and collide with the
atoms of the gas inside of the sphere. As a result of the collisions, some of
the atoms get raised to a higher energy level. Very quickly, usually about 10^-8
seconds, the excited atoms will return to their normal energy states.
This process involves the emission of a photon. Since the energy levels of a
particular substance are very quantified, the photon emitted will have a
particular energy. This particular energy produces light of a specific
wavelength and thus a specific color. Einstein showed that photons of energy E
will have a frequency, f, equal to E/h, where h is Planck's constant (6.63 x 10^
-34). The wavelength of the light can be found by wavelength = speed of light/
frequency. (from MadSci.org)

1. Turn off the lights so that you can see the plasma ball glowing.
2. Put your hand on the plasma ball. What happens?
3. Now bring the fluorescent light tube close to the plasma ball. What happens?
4. This step requires a friend, so have one close by
and ready to help. Stand on the chair or stool and put your hand on the
ball. Now have your friend hand you the light tube. Do you see it light
up? What happens if your friend lets go? Be careful to not touch the
ends of the light tube – it gets hot!
5. Put a penny on the top of the plasma ball.
Carefully touch the penny with another penny. Don’t use your finger –
you’ll get a shock!

What’s going on?
The plasma ball is a miniature Tesla coil. Inside the ball is a coil of
wires that have electrons going through them oscillating at a very high
frequency. This shakes the atoms around the wires so hard that their
electrons start to fall off! Inside the glass globe is a partial
vacuum. This just means that some of the air has been sucked out.
Because there is not as much air in there, it is easier to make
electric sparks that can be seen.

The electrons then travel out into the air from the glass ball. We know
this because the plasma ball lights up the light bulb. If you touch the
plasma ball, all of the electrons will go through you to the ground.
You see only one big spark inside the ball where you put your hand. If
you stand on a stool, you are insulated from the ground and get filled
with electrons. This means you can light up a fluorescent light bulb! (from University of Wisconsin)

Large plasma ball in action from the Ontario Science Center

What happens when you put a fluorescent light bulb next to a plasma ball?